The development of materials for tissue fixation devices has proceeded rapidly in recent years. The use of biodegradable polymers in such devices has provided surgeons with a safe alternative to metallic implants, potentially reducing adverse tissue response and eliminating the presence of a permanent tissue defect or the need to surgically remove the implant.
Ideally, biodegradable tissue fixation devices should provide long-term repair strength, complete healing of the defect site, and controlled resorption of the device by the body. Biodegradable tissue fixation devices should have sufficient mechanical strength to withstand loads encountered during the healing process, while also providing an open “scaffold” structure that allows full bone ingrowth and remodeling.
Thermally-induced phase separation of polymer solutions and blends has been used to form porous biodegradable scaffolds for tissue engineering (see, e.g., J Biomed Mater Res, 47:8-17, 1999 and J Biomed Mater Res 60:20-29, 2002.) For example, polymeric scaffolds may be formed by heat treating a blend of soluble and insoluble polymers to increase phase separation, and then dissolving the soluble polymer to leave a porous scaffold of the insoluble polymer. These scaffolds are formed prior to implantation, i.e., the scaffold is porous when it is implanted into a patient.
Porous ceramic materials, e.g., porous calcium phosphate ceramics, have been used as bone graft substitutes. While these materials may promote bone cell attachment and infiltration, they are typically brittle, and thus may not possess the mechanical strength needed for use in tissue fixation devices.